Beetles are one of the most diverse groups in the world, and the darkling beetles (Tenebrionidae) are the fifth largest family.
There are over 1,000 species of darkling beetles in the United States, spreading to other parts of North America, and over 20,000 known species worldwide.
However, while you may be familiar with a few darkling beetle species as adults, they’re more commonly known in larval form as mealworms or false wireworms.
Darkling beetles (sometimes referred to as litter beetles) get their name partly due to their primarily black or brown coloration, and partly because the majority of species are nocturnal.
What Are Darkling Beetles?
The family Tenebrionidae is a bane to gardeners in both larval and adult forms.
It undergoes a complete metamorphosis burning its life cycle, with the eggs, larva, pupae, and adults of a single species often looking completely unrelated to each other.
Adult beetles vary greatly in shape and size.
They may be oval, wide, long, curved, or flattened; and American species range from ⅛ to ¾” inches long and worldwide species ranging up to 1 ½” inches.
Their coloration ranges from rusty brown to blue-black or dull black.
Despite being so varied, darkling elves have certain physical similarities, including:
- A single sternite
- 4 tarsal claws on the hind legs with 5 on the rest.
- Antennae with 11 segments but different shapes.
- Frontal ridges on the eyes
- Dull sheen to the body instead of glossy
- Fused wings, usually smooth
Meanwhile, darkling beetle larvae tend to be longer than their adult forms, measuring on average between ⅓ and 1/2 “ inches long.
Their pale yellow to dark brown color often leads to confusing them with wireworms.
Darkling beetles tend to take up residence in sheltered spots near plant material. Some common places these scavengers prefer to hide under include:
- Dirt clods
- Fallen tree bark
- Wood chips
- Wood piles
What Damage Do Mealworms Cause?
These flightless ground beetles can do major damage in large numbers, but even a handful can cause problems.
The lesser mealworm will attack both seedlings and the foliage of many garden crops, including:
- Cucurbit flowers
- Pistachio flowers
Additionally, some species of mealworm beetle are known to transmit plant diseases and poultry parasites.
They will gather where there’s chicken feed or excess plant matter, such as compost piles.
A few species have earned the nickname flour beetle because they will attack stored grains.
Depending on the species, they may even damage insulation or wooden structures.
How To Control Darkling Beetle Pests?
Begin by removing leaf litter, weeds, or any other food source which might attract adult darkling beetles prior to planting.
Break up any dirt clods and keep fruit raised above ground.
Only plant seedlings once they’ve reached about 6” inches in height.
Avoid using alfalfa around a darkling beetle infestation and allow the land to go fallow periodically.
Add natural or chemical decomposers to speed up the composting of any organic matter above or below ground, including on fallow spaces
Wrap sticky tape around fruit trees to catch any beetles trying to climb to the fruit.
When possible, avoid using mulch or lava stone ground cover, as these provide more places for the beetles to hide.
Birds, lizards, and rodents all love to snack on darkling beetles, a fact that may prove either advantageous or problematic.
You may also choose to use an insecticide such as Zenprox EC to tackle an existing infestation.
When using any insecticide, be sure to check the label to ensure it covers darkling beetles or their larval stage.